Method of molding a latch opening

ABSTRACT

1. In the molding of a plastic container by forming a softened sheet of said plastic between a pair of mold parts, an improved molding operation for forming a latch opening in said container, said improvement comprising: (a) stretching said plastic sheet over a die surface arranged on one of said mold parts in the region of said latch opening; (b) pressing a former through said stretched plastic and into contact with said die surface to cut through said plastic along one edge of said latch opening as said mold parts close; (c) scraping said former along said die surface away from said cut int the region of said latch opening while said mold parts close further; (d) pushing said plastic across said scraped region away from said cut and into a compressed wall of said plastic having an edge spaced from said cut to form said opening; and (e) tearing said plastic along each side edge of said latch opening as said plastic is pushed across said scraped region by said former.

7 1 K. G. DAHLBERG 3,845,181

METHOD OF HOLDING A LATCH OPENING 2 Sheets-Sheet 1 Filed Sept. 25, 1972M M Q fi 1 2 O 4. 2 4 7 W F Q QM; OOO

FIG- 10 Oct. 29-, 1974 DAHLBERG 3,845,187

METHOD OF MOLDING A LATC H OPENING Filed Sept, 25, 1972 v 2 Sheets-Sheet2 United States Patent 3,845,187 METHOD OF MOLDING A LATCH OPENING KurtGunnar Dahlherg, Pittsford, N.Y., assiguor to Thermo-Trim, Inc.,Rochester, N.Y. Filed Sept. 25, 1972, Ser. No. 291,914 Int. Cl. B29c17/00 US. Cl. 264-154 4 Claims ABSTRACT OF THE DISCLOSURE A latchopening in a plastic container is formed during the molding of thecontainer. As mold parts close, a softened sheet of plastic is stretchedover a die surface on one of the mold parts, and a former carried by theother mold part is pressed into contact with the die surface to cutthrough the plastic along one edge of the latch opening. As the moldparts close further, the former scrapes along the die surface and pushesthe plastic across a scraped region away from the cut to form acompressed wall of plastic spaced from the cut to form the latchopening.

BACKGROUND OF THE INVENTION Molded plastic containers for eggs presentlyhave a cover that latches down over a base portion of the container, andsimilar latching containers are useful for packaging other fragile itemssuch as lightbulbs. The presently preferred latching arrangement forsuch containers requires a latch opening formed in the container cover,and since these containers have been formed by the millions in recentyears, the art of forming the containers and the latch openings is welldeveloped and settled. It includes heating a Wide, continuous sheet ofplastic material to soften it for molding, advancing the softened sheetrepeatedly in between the parts of a multi-cavity mold, pressing themold parts together to form the cartons while the mold parts are cooledto fix the plastic in its molded shape, separating the mold parts andrepeating the process indefinitely. The mold parts are large, complexand watercooled so there is no available space or opportunity forpunching out holes in the cartons during the molding operation. Hence, asubsequent punching step is required for forming the latch opening.

The molded cartons are fed from the molding station to a punchingstation where the cartons are registered with punching equipment thatincludes male and female dies actuated to punch out the latch openingsat the desired location in each carton. The slugs of punched-outmaterial are vacuumed away, and then the cartons are fed to a cuttingand trimming station that cuts them out of the large sheets andseparates them for stacking.

The hole punching equipment presently adds about $10,000 to the cost ofthe basic machine and also increases the size and weight of the machineconsiderably. Fairly precise equipment is required for registering thecartons accurately with the hole-punching equipment so that the latchopenings are properly spaced, and the punching dies must be accuratelymade and kept sharp to form clean cut openings. The hole punchingequipment causes many problems, and a significant percentage of cartonsmust be scrapped because of various malfunctions of this accessory.

THE INVENTIVE IMPROVEMENT The invention involves a realization of themany disadvantages of present hole-punching equipment to form latchopenings in molded containers and includes recognition of a way offorming the desired latch opening during the molding process itself witha relatively simple and workable variation in the mold to eliminate theentire holepunching accessory and the problems it causes. The aims ofthe invention are generally economy, efficiency, accuracy andreliability in forming latch openings in molded ice containers, and ithappens that the inventive molding operation forms a latch opening witha stronger latching ledge and an improved shape that is attractive inappearance, somewhat more convenient to operate, and more reliable as alatch.

SUMMARY OF THE INVENTION The inventive molding operation improves on theart of molding plastic containers from a softened sheet of plasticformed between a pair of mold parts. The improvement includes stretchingthe plastic over a die surface on one of the mold parts in the region ofthe latch opening, and pressing a former through the stretched plasticand into contact with the die surface to cut through the plastic alongone edge of the latch opening as the mold parts close. Then the formeris scraped along the die away from the cut while the mold parts closefurther, and the plastic is pushed across the scraped region away fromthe cut and into a compressed wall of plastic having an edge spaced fromthe cut to form the opening.

DRAWINGS FIG. 1 is a plan view of an egg carton having a latch to beformed according to the invention;

FIG. 2 is a fragmentary elevational view of the egg carton of FIG. 1 inclosed and latched condition;

FIG. 3 is a fragmentary cross-sectional view of the carton of FIG. 2taken along the line 33 thereof;

FIG. 4 is a fragmentary plan view of the latch of FIG.

FIG. 5 is a fragmentary plan view of a die used in the practice of theinvention;

FIG. 6 is a fragmentary cross-sectional view of the die of FIG. 5 takenalong the line 66 thereof;

FIG. 7 is a fragmentary cross-sectional view of a former cooperatingwith the die of FIGS. 5 and 6;

FIGS. 8 and 9 are elevational views of the former of FIG. 7;

FIG. 10 is an elevational view of a mounting support for the former ofFIG. 7;

FIGS. 11-14 are fragmentary, cross-sectional view of the operationalevents forming a latch opening according to the invention;

FIG. 15 is a plan view of an alternative preferred die for practicingthe invention;

FIG. 16 is a bottom view of the die of FIG. 15; and

FIG. 17 is an elevational view of a former shown in cooperation with aportion of the die of FIG. 15.

DETAILED DESCRIPTION Carton 10 of FIG. 1 is designed to hold a dozeneggs in base 11 with cover 12 closable over base 11 for latching downover the eggs. The invention is not limited to an egg carton, however,and container 10 can hold other items. The closing edge of base 11 hasthe latch flap 13, and cover 12 has latch openings 14 that interlockwith latch flap 13 to latch cover 12 closed. The invention involves animproved way of forming latch openings in cover 12 during the process ofmolding container 10, but before this process is explained, the latchitself will be described with reference to FIGS. 2-4.

Latch flap 13 has recesses or indentations 15 formed to provide alatching ledge 16. Cover 12 has a registering recess 17 fitting intorecess 15 in latch flap 13, and a latch opening 14 is formed throughcover 12 above recess 17. The upper or latching edge 18 of recess 17lies at the bottom of latch opening 14 and is shaped to slide underlatching edge 16 of latch flap 13 to latch cover 12 down over base 11. Alatch bar 19 above latch ledge 17 then fits into latch opening 14, andfinger pressure through opening 14 against bar 19 can be used to releasethe latching engagement between ledge 16 and edge 18. The upper edge 20of latch opening 14 is cut into the top of cover 3 12, and the sides 21of opening 14 extend over the corner of cover 12 and down to the levelof latching edge 18.

The basic latch as described above is generally known in the art. Theinvention involves a way of forming latch opening 14 in cover 12 duringthe molding operation to eliminate the separate step presently requiredfor punching out opening 14. The inventive molding operation is bestshown in FIGS. -14.

Mold part 22 for forming the interior of cover 12 carries a die 23inlaid into the portion of mold part 22 that forms the upper corner ofcover 12. Die 23 is held in place by screws 24 at the desired region forforming latch openings. A chamfered edge 25 along the top of die 23outlines the upper boundary of the desired latch opening, andprojections 26 extend downward along the sides of the desired opening. Asurface 27 leads downward from chamfer 25 and is oblique or inclinedrelative to the closing direction of mold part 22. A recess surface 28below surface 27 forms the interior of recess 17 in cover 12.

Mold part 29 of FIG. 7 mates with mold part 22 to form the outside ofcover 12 and carries a former 30 for forming the latch opening. Former30 has a slot 31 engaged by a retainer plate 32 recessed into mold part29 and held in place by screws 33. Retainer plate 32 holds former 30against motion vertically in the direction of mold closure, but allOWslimited transverse motion in opening 34 formed in mold part 29. Amounting plate 35 screwed to mold part 29 has a recess 36 facing former30. An elastomeric block 37 formed of a material such as rubber issecured in recess 36 in any suitable way such as by adhesive, and block37 preferably has holes 38 allowing it to be compressed in recess 36.Block 37 engages and biases former 30 against retainer plate 32 toextend fully into the cavity portion of mold part 29, but former 30 canmove transversely to the closing direction of mold part 29 to compressblock 37.

Former 30 has a cutting edge 39 that registers with chamfer 25, andbelow cutting edge 39, former 30 has a tapered projection 40 that shapesthe outside of recess 17 in cover 12. The operation of former 30relative to die 25 to form the desired latch opening in container isshown schematically in FIGS. 11-14.

A sheet of plastic material 41 is heated and softened and fed betweenmold parts 22 and 29 for forming container 10. The open condition ofmold parts 22 and 29 is shown in FIG. 11. As the mold parts close,plastic sheet 41 is stretched over die 25 as best shown in FIG. 12, asformer 30 approaches die 25. Before mold parts 22 and 29 are fullyclosed, cutting edge 39 of former 3t) presses through plastic sheet 41and into engagement with chamfer 25 to cut through plastic 41 and formupper edge of opening 14 as shown in FIG. 13. Resilient mounting blocks37 supporting former 30 allow limited movement of former 30 relative tomold part 29 so that cutting edge 39 moves into precise registry withchamfer for a clean cut around the upper edge of the desired latchopening.

As mold parts 22 and 29 move to the fully closed position shown in FIG.14, cutting edge 39 of former scrapes over chamfer 25 and moves downinclined or oblique surface 27 to near the lower edge of die 23. Thiscauses cutting edge 39 and the adjacent ledge 42 of former 30 to scrapealong surface 27 and remove plastic 41. The scraped plastic 41 is pusheddownward into a compressed wall of material 43 the upper edge of whichforms latching edge 18. The scraping action of former 30 along obliquesurface 29 moves former 30 transversely of the mold closing direction inthe direction of the arrow of FIG. 14 to compress resilient supportblock 37. When mold parts 22 and 29 reopen, support block 37 pushesformer 30 back to its normal position fully extended into the cavity ofmold part 29.

Projections 26 as shown in FIGS. 5 and 6 straddle former 30 to supportplastic material 41 along the side edges of the scrapedflut latchopening. Plastic 41 is stretched thin over projections 26 to formtear-lines along the side edges of the latch opening, and former 30tears plastic 41 along projections 26 and scrapes along the sidesurfaces of projections 26 to tear and clear away the plastic along theside edges of latch opening 14.

The relatively soft plastic material 41 is easily cut and scraped byformer 30 to form a clean-cut latch opening 14, and cutting and scrapingin the molding operation assures accurate positioning of latch opening14. The compression of plastic material 41 in wall 43 forms a muchstronger and tougher edge 18 for more secure latching of the carton. Die23 and former 30 are preferably formed of hardened steel material thatwears well and are made relatively simply for economical construction.Former 30 is self-aligning with die 23 for high accuracy with tolerablelimits.

There are many other ways that a suitable former and die can be mountedin mold parts for forming a latch opening according to the invention.Also, dies and formers can have many different shapes that accommodatethe preferred cutting and scraping motion to form a mo'ded latchopening. One preference in this is that the die have an oblique surfacescraped by the former, and relative motion between the die and formertransverse to the mold closing direction is necessary to accommodatescraping motion along an oblique surface. The relatively movable partcan be arranged in either half of the die, however, and former 30 neednot be resiliently movable as shown in FIG. 7.

For example, the preferred embodiment of FIGS. 15- 17 uses a relativelyfixed former 50 shaped similarly to former 30 and relatively movableparts in die insert 51. Die insert 51 is inlaid in the mole portion ofthe mold at the latch opening region, but its working edges are movableand resiliently biased.

Die part 52 is movable in a slot 53 transversely to the mold closingdirection to move toward and away from former 50. A spring or otherresilient means engages a pin 54 on die part 52 to bias die part 52resiliently toward former 50. Die part 52 has a chamfered upper edge 55that engages edge 56 of former 50 for cutting the upper edge of thelatch opening as previously described, and as cutting edge 56 of former50 moves downward during further mold closure, edge 56 scrapes alonginclined or oblique surface 57 of die part 52 to scrape plastic awayfrom the central latch opening region. Die part 52 moves transversely asmall amount to allow downward motion of cutting edge 56, and upstandingridge along the upper edge of die part 52 thins the plastic for a bettercut.

A pair of side projections 58 are movable in transverse slots 59 and arebiased inward toward each other by springs or other resilient meansengaging pins 60. The inward facing surfaces 61 of projections 58 aredownwardly convergent by a slight angle so that the sides of former 50fit snugly between projections 58 and spread projections 58 slightly asformer 50 drives down between surfaces 61. This provides a cleanscraping along the side edges of the latch opening, and projections 58stretch the plastic out in a thin tear-line along the side edges of theopening so that accurate tearing accompanies the scraping. Also, ridges65 on top of projections 53 thin the plastic for a cleaner edge cut.

There are many other ways that die inserts and formers can be fittedinto mold parts for scraping away plastic material to form a latchopening according to the invention, and those skilled in the art willappreciate many different mountings, spring and other resilient biases,and different preferred shapes for cutting edges, forming tearlines, andscraping away plastic as mold parts close. Any suitable arrangement ishighly valued for eliminating the hole-punching accessory with itsalignment, burr, and other problems. Latch-hole molding according to theinvention, also forms a compressed and stronger latching edge, perfectregistration of the latch opening with the latch ledge, and a smallerand more attractive latch opening rather than a larger, punched-outopening that is oversized to accommodate misalignment problems.

Persons wishing to practice the invention should remember that otherembodirnents and variations can be adapted to particular circumstances.Even though one point of view is necessarily chosen in describing anddefining the invention, this should not inhibit broader or relatedembodiments going beyond the semantic orientation of this applicationbut falling within the spirit of the invention. For example, thoseskilled in the art will appreciate the shapes, configurations,constructions, mounts and bias means suitable for forming latch openingsaccording to the invention.

I claim:

1. In the molding of a plastic container by forming a softened sheet ofsaid plastic between a pair of mold parts, an improved molding operationfor forming a latch opening in said container, said improvementcomprising:

-(a) stretching said plastic sheet over a die surface arranged on one ofsaid mold parts in the region of said latch opening;

(b) pressing a former through said stretched plastic and into contactwith said die surface to cut through said plastic along one edge of saidlatch opening as said mold parts close;

(c) scraping said former along said die surface away from said cut inthe region of said latch opening while said mold parts close further;

(d) pushing said plastic across said scraped region away from said cutand into a compressed wall of said plastic having an edge spaced fromsaid cut to form said opening; and

(e) tearing said plastic along each side edge of said latch opening assaid plastic is pushed across said scraped region by said former.

2. The improvement of claim 1 including stretching said plastic oversupports along the sides of said scraped surface to aid in tearing saidplastic along said supports to form said torn side edges for saidopening.

3. The improvement of claim 1 including moving said scraped plasticobliquely relative to the closure motion of said mold parts so saidcompressed wall and said out edge of said latch opening are laterallyspaced apart relative to said closure motion.

4. The improvement of claim 3 including stretching said plastic oversupports along the sides of said scraped surface and tearing saidplastic along said supports to form side edges for said opening.

References Cited UNITED STATES PATENTS 3,418,690 12/1968 Edwards 2641633,414,941 12/1968 Ignell 425310 ROBERT F. WHITE, Primary Examiner T. E.BALHOFF, Assistant Examiner US. Cl. X.R. 264-163 UNITED STATES PATENTAND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 45,1 7 Page1 of 2 9 DATED I October 29, 1974 INVENTOR(S) 1 Kurt G. Dahlberg It iscertified that error appears in the above-identified patent and thatsaid Letters Patent is hereby corrected as shown below:

Column 5, line 22, after "opening" should read said die surfaceextending for the width of said latch opening and along the side edgesof said latch opening Column 5, line 25, "along one edge" should readfor the Width Column 6, line 3, before "tearing" should read said formerengaging said die surface along said side edges of said latch openingfor Column 6, line 6, after "1" should read wherein said die surfaceincludes ridges along said side edges of said latch opening and Column6, line 7, "supports along the sides of said scraped surface" shouldread said ridges V Column 6, line 8, delete "supports to form saidtorn".-

Column 6, line 15, after "3" should read wherein said die surfaceincludes ridges along said side edges of said latch opening and alongsaid out and v UNITED sTATEs PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3,845,187 Page 2 of 2 DATED I October 29, 1974INVENTOR( 1 Kurt G. Dahlberg It is certified that error appears in theabove-identified patent and that said Letters Patent is hereby correctedas shown below:

Column 6, line 16, supports along the sides of said scraped surface and"should read said ridges to aid in forming said cut and Column 6, line17, delete "supports to form".

Signed and Scaled First Day Of September I98] [SEAL] Arrest:

GERALD .I. MOSSINGHOFF Arresting Ojficer Commissioner of Paten ts andTrademarks

1. In the molding of a plastic container by forming a softened sheet ofsaid plastic between a pair of mold parts, an improved molding operationfor forming a latch opening in said container, said improvementcomprising: (a) stretching said plastic sheet over a die surfacearranged on one of said mold parts in the region of said latch opening;(b) pressing a former through said stretched plastic and into contactwith said die surface to cut through said plastic along one edge of saidlatch opening as said mold parts close; (c) scraping said former alongsaid die surface away from said cut int the region of said latch openingwhile said mold parts close further; (d) pushing said plastic acrosssaid scraped region away from said cut and into a compressed wall ofsaid plastic having an edge spaced from said cut to form said opening;and (e) tearing said plastic along each side edge of said latch openingas said plastic is pushed across said scraped region by said former.